The present invention relates to telemetric systems and in particular to systems employing an elongated coil.
Conventional telemetry has employed a radio frequency (r.f.) link to relay data from a missle. Such systems employ a plurality of subcarriers at different frequencies, each frequency being modulated by an associated transducer that measures a parameter of the missile, such as the acceleration or stress. These subcarriers are combined and used to modulate an r.f. carrier which is then transmitted from the missile by means of an antenna. A conventional ground receiving station receives the r.f. carrier and separates the various subcarriers by using well-known frequency division demultiplexing techniques. A disadvantage with equipment of this type is that the circuitry required to process r.f. signals can be expensive and unreliable. Moreover, gun gas or other interfering atmospheric conditions can effectively block transmission of r.f. energy. In addition destructive interference caused by reflection of r.f. energy from the gum can interrupt transmission. In the situation where the telemetric data need only travel a relatively short distance and is only transmitted for a short interval, the expense and unreliability associated with a conventional r.f. link is unnecessary.
The present invention provides a reliable, efficient and inexpensive telemetric system by employing an elongated conductive coil whose length corresponds to the distance traveled by a missile during the transmission of a burst of transducer data. This coil is located adjacent to a muzzle to obtain data immediately upon the exiting of the missile therefrom. An associated transmitting means employs a modulator which is driven by a transducer through a delay means. The modulator drives a missile coil at a carrier frequency of less than one megaHertz, preferably. Using equipment of this nature, expensive and unreliable high frequency techniques are avoided and potential interference such as ionized gun gas does not block the telemetering function. In addition destructive interferences caused by the reflections from the gun tube is reduced considerably by using relatively long wavelengths (low frequency).